A plastic optical fiber is known wherein an amorphous fluorinated polymer is used as the material forming a core and a clad, and a protective coating layer is provided outside the clad (Patent Documents 1 and 2). Patent Documents 1 and 2 disclose that in the core, an amorphous fluorinated polymer having no C—H bond is used as a matrix, and a compound having a refractive index different from the matrix is distributed with a concentration gradient in the radial direction to form a gradient index structure.